Melt the butter in a heavy, medium-size sauce-pan. Add the lemon juice and water and mix. Add the sugar and stir until it is dissolved. Bring the mixture to a boil, stirring occasionally, and boil it gently for 7 minutes. Remove the pan from the heat and let it sit for a couple of minutes until the syrup has stopped boiling. Whisk in the cream until the mixture is smooth and pour the sauce into a bowl or pitcher.

Remove pits from peaches and slice. Place in bowls for serving. Pour sauce over fruit and sprinkle lightly with Fleur de Sel.